The Sun has been a source of inspiration and awe for a very, very long time. It can not be known how long ago people noticed that the Sun can warm the body or where a person lived but it can be safely said that it was well before any written language.
Solar Heating has been around for almost as long as we have build dwellings to live in. Here in Colorado we have Mesa Verde cliff dwellings that used the sun to keep warm in the Winter and cool in the Summer. These dwelling made use of Passive Solar gain rather than actively harnessing the Sun’s energy by building their homes in a cliff niche.
Around 400 BCE the Greeks made use of Passive Solar Energy by constructing their buildings to take advantage of the free heat the Sun provided and when glass was invented used windows that kept the heat gain indoors for a longer period. A quick timeline of the use of Solar Energy:
- 3rd Century BCE Greeks and Romans used mirrors to concentrate the Sun’s energy to light torches and fires.
- 2nd Century BCE Greeks used mirrors to set fire to enemy ships.
- 20 CE a Chinese document talks about using mirrors to light ceremonial fires.
- In the first 4 centuries of the Common Era Romans used large south facing windows to help keep bathhouses warm.
- 6th Century CE the Justinian Code gave everyone right to the Sun and equal access – no one could block another’s access to the sun
- 1200 CE cliff dwelling like those in Colorado made use of south facing dwelling to harness the Sun passively.
- Horace de Saussure in 1767 created the first solar box collector used by Sir John Herschel in South Africa to cook his meals.
- 1839 Edmond Becquerel after immersing two dissimilar metals in an electrolyte found that when exposed to the Sun produced more electricity thereby discovering the photovoltaic effect.
- …and the number of discoveries only accumulate too numerous to list here.
Although not complete it gives someone the insight that harnessing the Sun’s energy (namely heat) has been something we has been done for a very long time.
Using the sun to cool on the other hand is a newer idea. The idea first started with Michael Faraday (1791 to 1867) who was the first to suggest and use a liquid that when allowed to vaporize cooled. The liquid he chose, and which later became used wide spread in early refrigerators, was ammonia. After compressing ammonia it was allowed to vaporize which gave the cooling effect he was looking for, and was the start of cooling and refrigeration.
In a solar collector system the Sun’s heat is used to bring a liquid to a boil and as it vaporizes it giving the same cooling effect without a compressor. Currently there are two types of solar cooling devices on the market. The first makes use of the traditional compressor driven by electricity from a Photovoltaic panel to create the cooling process. The other model makes use of evaporative cooling or absorption chillers.
Another way I recently found that comes out of Germany is the use of traditional Solar Heat Absorption Panels and Photovoltaic Panels. Both provide energy to the home year round. The heat first goes into a tank to be stored until needed. Once the tank is fully charged the heat energy is not ignored or wasted but instead a heat pump is used to move the extra heat into the ground beneath the home to store it. It is a kind of heat battery except slightly more efficiently. To heat the home the Sun’s energy can be used directly, or the heat in the tank and finally the heat stored in the ground. To cool the home a second heat pump is used to draw heat from the house which is then moved directly beneath the home for storage. This set up, and this is from what I have gathered and has not been fully tested for any length of time as far as I know, is far more efficient than running air conditioners or chillers and direct heating in the winter. This method is called a Geosolar system.
Because the ground is used as both a source of heat and to store excess heat the whole system becomes more efficient. The big issue with possible freezing of the ground which can happen as more heat is drawn out than is available is eliminated by putting heat back into the ground in warmer months. Because both the heat source and electricity come from a renewable source of energy the efficiency of this system is in the neighborhood of 500%. That means you are getting more out than is being put in as with a traditional ground based heat pump which ranges from 200 to 300% efficiency. Not bad when a system like this is combined with a PassivHaus design that already has greatly reduced heating and cooling needs to begin with. With a PassivHaus such a system would actually become a secondary backup source of heating and cooling adding to its overall efficiency.
With a home and a system that are both with such high efficiency will allow it to last much longer than a traditionally designed system used only for supplemental heating or cooling needs. Combining technologies is the answer because each efficiency is piggy backed on adding to the overall efficiency of a system.
Resources:
http://en.wikipedia.org/wiki/Geothermal_heat_pump
http://www.heliossouth.com/documents/Brief%20History%20of%20Solar%20Cooling.pdf
http://www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf
Greenhouse Project Denver 